1. Field of the Invention
The present invention relates to a semiconductor substrate, an electronic device and a method for manufacturing the same.
2. Description of the Related Art
Recently, there has been proposed a TSV (through-silicon-via) technology of providing a circuit substrate with a large number of through-electrodes and stacking such circuit substrates. With the TSV technology, many functions can be packed into a small footprint and important electrical pathways between elements can also be dramatically shortened to increase processing speed.
When using the TSV technology, the through-electrodes must be electrically insulated from a silicon substrate. As means for electrical insulation, Japanese Unexamined Patent Application Publication No. 2008-251964 discloses a technology of forming a ring-shaped isolation groove passing through a silicon substrate in such a manner as to surround a through-electrode passing through the silicon substrate, forming a silicon film directly on the bottom surface and the side surfaces of the isolation groove, then forming an insulation film on the silicon film in such a manner as to fill up a gap left in the isolation groove, and thermally oxidizing each surface of the silicon film in contact with the inner or outer peripheral side surface of the isolation groove into a thermally-oxidized silicon film.
However, since it requires the steps of forming a silicon film directly on the bottom surface and the side surfaces of the isolation groove, forming an insulation film on the silicon film in such a manner as to fill up a gap left in the isolation groove after formation of the silicon film, and then thermally oxidizing the surface of the silicon film, the process inevitably becomes complicated and time-consuming. When replacing the conventional planar arrangement with the TSV technology, cost performance is important from the viewpoint of industrial mass production, but the above related art cannot meet this need sufficiently.
Moreover, since it is configured to electrically insulate the through-electrodes and the silicon substrate with the thermally-oxidized silicon film, it is difficult to form a sufficiently thick insulating film and therefore it is difficult to decrease capacitance for the through-electrodes, which results in limiting improvement in signal transmission properties and reduction of power consumption.
Furthermore, since it is difficult to form a sufficiently thick insulating film, the effect of relaxing a stress occurring in the vicinity of the through-electrodes with the insulation film can be hardly expected. Therefore, the semiconductor circuit elements have to be located away from the through-electrodes, reducing area efficiency.
On the other hand, Japanese Unexamined Patent Application Publication No. 2004-31923 discloses technical details of forming a separating trench groove for a MOS capacitor or a bipolar capacitor. The disclosed information is roughly as follows.    (a) A suspension having insulating particles such as silica particles dispersed in a disperse medium such as an organic solvent is applied to a trench-having surface of a silicon substrate by spin coating, and then, the disperse medium is removed from the applied film to fill the trench with the insulating particles. The insulating particles are bonded neither to each other nor to the side walls and bottom surface of the trench. Then, the top of the trench is closed by a reflowable dielectric layer, preventing the insulating particles from escaping from the trench.    (b) Also disclosed is a particulate insulating layer in which after the insulating particles are filled in the trench in the same manner as in the above (a), the insulating particles are bonded to each other through an insulating binder to form a network structure of the insulating particles and the insulating binder. It describes that an inorganic or organic SOG obtained by dissolving a silanol in an organic solvent can be used as a material for the insulating binder. Also disclosed is that —OH and —O— bonded to an Si atom in the silanol used for the inorganic or organic SOG can be partially replaced with —H, that —CH3 in the silanol used for the organic SOG can be replaced with other alkyl groups such as —C2H5, that —OH and —O— bonded to an Si atom in the silanol used for the organic SOG can be partially replaced with alkyl groups such as —CH3 and —C2H5, and so on.    (c) A first particulate insulating layer containing no binder and a second particulate insulating layer containing a binder are combined to provide an insulating layer. The top of the first particulate insulating layer containing no binder is covered with the second particulate insulating layer containing an insulating binder.    (d) A particulate insulating layer forming an insulating layer includes first and second insulating particles that are homogeneously mixed together and an insulating binder for cross-linking them.
In Japanese Unexamined Patent Application Publication No. 2004-31923, however, since the insulating particles such as silica particles are bonded neither to each other nor to the side walls and bottom surface of the trench, it is required to employ the technique of closing the top of the trench with a reflowable dielectric layer (see the above (a)) or the technique of bonding the insulating particles through a binder (see the above (b) to (d)), complicating the insulating structure and the manufacturing process.
In the case of the above technique (a), moreover, it is impossible to form an insulating layer having a high adhesion strength to the silicon substrate. In the case of the technique (b), since the particulate insulating layer has a network structure formed from the insulating particles and the insulating binder, the adhesion strength of the insulating layer to the silicon substrate is not sufficient, either. When using a binder such as an organic SOG, on the other hand, since the insulating layer contains carbon, it is not inherently desirable as an insulating layer that requires high insulation resistance. In the techniques (c) and (d), since the first and second insulating particles are included, the problem still remains regarding the adhesion strength.
When insulating a vertical conductor forming the through-electrode or the like, furthermore, the vertical conductor may be embedded in the insulating layer itself, but such an insulating structure cannot be dealt with by the technology described in Japanese Unexamined Patent Application Publication No. 2004-31923.